The card is measuring in at a case-busting 305mm long, features two, full-fat Caymen XT GPUs, the same as those found in AMD’s fastest single-GPU card. The Radeon HD 6970 2GB. This means that it boasts a whopping 3,072 stream processors and as each GPU is serviced by 2BG of GDDR5 memory, there’s 4GB of memory on the card. The card’s clock speeds are a little lower than those of the HD 6970 2GB by the memory at 1,25GHz. That’s a colossal amount of graphics horsepower for a single card to contain.

However, by using such high-performance GPUs, AMD has presented itself with a challenge in powering and cooling this beast. The company had to break the rules of how to power a graphics card as well as investigate new technologies in order to make the HD 6990 4GB a safe and reliable card to use.

For a star the HD 6990 4GB take the PCI Express 2.0 specifications which limits expansion cards to consuming 300W of power, and chucks in out the window. By default, the HD 6990 4GB draws up to 375W of power- up to 75W from the motherboard and 150W from each the two 8-pin PCI-E power connectors on the top of the card. While this means that HD 6990 4GB is effectively non-compliant with the PCI-E 2.0 standard, AMD started that breaking the 300W limit had been ‘ a matter of time’ and that it was ‘not worried’ by any potential ramification. Regardless, you’ll need a powerful PSU to power the HD 6990 4GB especially, if u want to investigate its unique overclock mode.

As with other Radeon HD 6990-series cards, the HD 6990 4GB has two vBIOSes. However rather than use the second BIOS as a back up should the primary BIOS faild during an update. AMD has chosen to load it with pre-overclock, boosting the GPU’s clock speeds from 830MHz to 880MHz.

To achieve this, the witch- named the Antilles Unclocking Switch-increases the vcore of the two GPUs by 0.055V, meaning that the card’s power consumption increases from 375W to a staggering 450W. AMD told us told that this decision was made due to the fact that low-end PSUs will probably struggle to deliver enough power over the two 8-pin PCI-E power connectors for the overclocked mode, but we’re unimpressed by the fact that AMD classes the use of the second BIOS as a warranty-voiding overclocking.

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One of the biggest problems with the card from the outset is its sheer size. At 305mm in length, it’s far too big for most PC chassis. But if your looking to drop this much cash on such a card, you can probably afford a new case

In order to take advantage of the Antilles Unolocking Switch’s capabilities you’ll first need to ensure your PSU has a capable 12V rail to deliver the over-spec voltage. The next step is invalidating your warranty by throwing the switch